DESCRIPTION: The applicant's research group has provided data which suggests that dietary protein is a potent regulator of calcium metabolism in young healthy women, an age group in whom the interaction of dietary protein and calcium metabolism has not been extensively studied. The PI reports that in this age group, within 4 days of the introduction of a high protein diet, hypercalciuria develops as a consequence, in part, of hyperparathyroidism with marked elevations in serum parathyroid hormone and 1,25(OH)2 vitamin D. Significantly, N-telopeptide, a marker of bone resorption, paralleled dietary protein intake such that this marker for bone resorption was lowest on the low protein diet, and highest when dietary protein was high. The above data supports the concept that dietary protein influences bone turnover in young women. The applicant now intends to study these relationships in postmenopausa women who are at a highest risk for osteoporosis. The goal of the proposed research is to quantify the effect of manipulating dietary protein on calcium kinetics and bone metabolism in young and older women. The PI will employ stable isotopic techniques in order to measure the effects of protein on calcium flux across the intestine and on bone accretion and resorption. Twelve healthy adult women (6 young and 6 older) will consume well-balanced, ten-day, experimental diets containing low, medium, and high levels of protein while calcium kinetics and bone turnover are assessed. The above experiments should help to clarify the effects of dietary protein on calcium absorption and bone turnover and allow for a more precise determination of the levels of protein intake which are necessary to optimize skeletal health in women.